When working a piece of material with a milling machine or similar type of work tool, the machinist must first identify a reference or starting point from which the various dimensions and locations for the milling work to be performed on the workpiece will be measured. Failure to properly identify the reference point results in the waste of time and material because of improper milling. Once found, this reference or starting point on the workpiece is then set in corresponding relationship with the centerline of the working part of the milling, drilling, lathe machine or other work tool so that the work will be performed at the correct location. The most common reference point utilized by most machinists is the edge of the workpiece. From the edge of the workpiece, dimensions are utilized to properly position the workpiece under the machine so that the work operation is performed at the desired location.
A common method utilized to find an edge of a workpiece is generally referred to as the contact or bump method. In this method, a simple piece of round stock is placed in the mill spindle and the work tool is hand cranked to gently abut the edge of the workpiece against the round stock. To align the work machine with the edge of the workpiece, the machinist then raises the round stock above the workpiece and moves the workpiece over half the diameter of the round stock. The micrometer dial setting at this position is zeroed to correspond to the edge of the workpiece, thereby aligning the work tool (i.e., the spindle centerline) with the plane running through the edge of the workpiece. Although the contact or bump method is quick and simple, it is well known that it is generally not accurate due to the inherent problems associated with trying to recognize when the contact occurs and the elasticity of the materials involved. In addition to the inherent accuracy problems, it is not uncommon for machinists, particularly relatively inexperienced or hurried machinists, to forget to take into account the one-half of the diameter of the round stock used as the edge finder. Another problem is that too much contact against the workpiece can dent or otherwise damage the workpiece. Moreover, this method is not intended or useful for finding the Z-plane edge of a workpiece.
Another technique uses a tool commonly known as a wiggler. Most wiggler sets come with an edge finder component that has a generally mushroom-shaped disk contact at the end of the wiggle shank opposite that which fits into the collet, typically in a ball-and-socket type of arrangement. As with the contact technique, the workpiece is moved towards the spinning edge finder until it gently touches the disk contact and steadies the wiggling. The workpiece is then slowly dialed further towards the edge finder until it is spinning true (i.e., no wiggle). At the point the edge finder starts to slip sideways from the drag of the spinning disk against the workpiece, the machinist has found the edge of the workpiece. As with the contact method, the machinist then raises the edge finder and dials in half of its diameter, typically 0.100 inches, to align the spindle centerline with the edge plane of the workpiece. Although the wiggler edge finder is generally considered to be accurate for routine machine work and good enough for most precision work, it is known to be frustrating to utilize due to the fact that it has to be reset for each edge contact, requires additional calculation, and may damage a workpiece. The wiggler device is not configured or useful for finding the Z-plane edge of a workpiece.
Another well known mechanical edge finder utilizes a spring loaded conical disc that spins while free of the workpiece and then suddenly kicks or slips sideways when contact with the edge of the workpiece is obtained. Unlike the wiggler edge finder, however, the disc of this type of edge finder only slips a certain amount and then goes no further. As a result, the machinist can back up and try again without having to reset the contact by hand. Once the edge is found, the machinist moves the workpiece, generally by moving the mill table, over one-half the diameter of the edge finder to align the spindle axis with the plane of the workpiece edge. This type of device is less precise and may damage a workpiece, as well failing to find the Z-plane edge of a workpiece.
A number of prior art edge finders are described in issued patents. For instance, U.S. Pat. No. 3,999,299 to Johnson describes an edge finder having a housing adapted to be received by the chuck on a work tool spindle, a slide biased against the housing by a spring that permits lateral movement of the slide and an outwardly extending finger that is rotatably attached to the slide at one end and shaped with a flat face at the other end to engage the side or edge of the workpiece. The plane of the flat face is configured to be in alignment with the axis of the work tool. Like the prior art devices set forth above, the workpiece is moved towards the edge finder until the edge is brought into contact with the flat face, at which time the slide moves at a right angle to the direction the workpiece is traveling indicating alignment with the edge. Unlike the above devices, however, no measurement adjustment is required. But the movement and device-specific ball-bearing friction results in a loss of precision. This type of device is not configured or useful for finding the Z-plane edge of a workpiece.
U.S. Pat. No. 5,217,336 to LeBlanc discloses an edge finder having an elongated body with a push pin at the semi-circular cross-section lower end that is contacted by the edge of the workpiece to operatively engage a lever connected to a dial indicator. The plane of the flat side of the lower end, which comes into contact with the workpiece edge when the pin is fully engaged, is in alignment with the axis of the spindle, thereby eliminating the need to factor in an adjustment. This device requires significant set-up and is prone to machinist error—particularly in cases of inexperience and hurriedness—making the device highly impractical. This type of device is not configured or useful for finding the Z-plane edge of a workpiece.
U.S. Pat. No. 4,429,463 to Angell discloses an electro-mechanical datum point locator tool that utilizes a cylindrical tip assembly that has an electrically conductive sleeve which causes a light to be emitted from the circumference of the tool's cylindrical housing when contact with the edge of the workpiece is obtained. The machinist must adjust for one-half the diameter of the tool's tip and requires the workpiece to be made of a conductive material—eliminating a large number of highly popular work materials. This type of device is not configured or useful for finding the Z-plane edge of a workpiece.
U.S. Pat. No. 5,276,975 to Fisher describes an audible-visual edge finder having a working end member at the end of a cylindrical shank. The working end member has a flat that is configured to make an audible sound when it contacts the workpiece and to cause the finder to vibrate radially, thereby enhancing the sideways jump, to visually signal contact with the workpiece. Like the above technique, the machinist must adjust for one-half the diameter of the working end member. This type of device is not configured or useful for finding the Z-plane edge of a workpiece.
U.S. Pat. No. 7,140,118 to Adrian describes an edge finding device that utilizes a downward-facing beam of light to visually locate the edge of a workpiece. The finder eliminates the need for calculations to find the edge and the risk of contact damage to the workpiece or precision tool. The device suffers from inaccuracy due to light dispersion when locating and touching the edge of the workpiece. It is also significantly more expensive to produce when compared to commonly used mechanical edge finding devices. This type of device is not configured or useful for finding the Z-plane edge of a workpiece.
As such, there exists a need for an edge finder that overcomes the limitations of the prior techniques, as well as accounting for Z axis measurements.